About the same time--that is to say, in the ninth century--cities began to rebuild their ancient walls; for the barbarian kings who had everywhere levelled these walls to the ground no longer opposed their reconstruction, and the danger of being invaded by the rival princes who disputed the throne made them necessary; besides, at this epoch new swarms of barbarians from all parts infested Europe; the inhabitants of Scandinavia, under the name of Danes and Normans, ravaged England and France; the Hungarians devasted Germany and upper Italy; the Saracens, masters of Africa, infested the southern coasts of Italy and the isles: conquest was not the purpose of any of these invaders; plunder and massacre were their only objects. Permission to guard themselves against continual outrages could not be withheld from the inhabitants of towns. Several thousand citizens had often been obliged to pay ransom to little more than a hundred robbers; but, from the time they were permitted by their emperors to rebuild their walls, to purchase or manufacture arms, they felt themselves in a state to make themselves respected. Their long suffering had hardened them, had accustomed them to privations and danger, and had taught them it was better to defend their lives than yield them up to every contemptible aggressor; at the same time, the population of cities, no longer living in idleness at the expense of the provinces of the empire, addicted themselves to industry for their own profit: they had, accordingly, some wealth to defend. The ancient curiæ and municipalities had been retained in all the towns of Italy by their barbarian masters, in order to distribute more equally the burdens imposed by the conquerors, and reach individuals more surely. The magistrates were the chiefs of a people who demanded only bread, arms, and walls. In the meantime the dukes, marquises, counts, and prelates, who looked on these cities as their property, on the inhabitants as men who belonged to them, and laboured only for their use, soon perceived that these citizens were ill disposed to obey, and would not suffer themselves to be despoiled, since they had arms, and could defend themselves under the protection of their walls: residence in towns thus became disagreeable to the nobles, and they left them to establish themselves in their castles. They became sensible that to defend these castles they had need of men devoted to them; that, notwithstanding the advantage which their heavy armour gave them when fighting on horseback, they were the minority; and they hastened to enfranchise the rural population, to encourage their growth, to give them arms, and to endeavour to gain their affections. The effect of this change of rule was rapid: the rural population in the tenth and eleventh centuries increased, doubled, quadrupled in exact proportion to the land which they had to cultivate.